The present invention relates to an electrical connector for printer circuit boards and, more particularly, to a high-speed controlled impedance connector for electrically connecting two circuit boards together.
Developments in switching and signal line equipment for telecommunications and data communications demand ever higher performance from all data transmitting components. Typically, a very large xe2x80x9cmother boardxe2x80x9d or back panel, is populated with connectors into which xe2x80x9cdaughter boardsxe2x80x9d are inserted. The signal from one daughter board proceeds into the back panel, through the back panel, and into another daughter board or cable. Some signals travel from point to point through a single conductor and some signals travel through a differential pair. There is a tight requirement for preserving signal integrity and to minimize the cross-talk and skew in such transmission lines, whether in the PCB or connector.
U.S. Pat. No. 5,993,259 issued to Stokoe et al disclose an electrical connector of such application. The connector disclosed in the ""259 patent includes a plurality of modularized chicklets bounded together. As shown in FIG. 4 of the ""259 patent, the terminals are stamped from a metal sheet, then embedded within an insulative material to form the chicklet. However, it can be readily seen from FIG. 4 that the length of each terminal is different from its adjacent terminal because of the right-angle arrangement. In addition, it would be unlikely to make two adjacent terminals with equal length. As long as the terminal length is different from one another, skew between terminals is therefore inevitable.
In addition, it will be difficult to have two adjacent terminals to be configured as a differential pair. By the way, because of the shape of the terminals, it is also unlikely to reach equal impedence between two adjacent terminals.
U.S. Pat No. 6,083,047 issued to Paagman discloses an approach to make a high-density connector by introducing the use of printed circuit board. According to teaching of the ""047 patent, conductive traces are formed on surfaces of the printed circuit board in a mirror-image arrangement, typically shown in FIG. 12. Again, the conductive traces formed on the surface of the printed circuit board are unlikely to have the same length. Skew is still inevitable.
In addition, in the above-described patent, distance between two adjacent terminals is too close to intercept a ground contact or conductive trace.
In the ""259 patent, even a ground bus is provided, however, the ground bus only electrically separate two adjacent chicklets, while it can not separate two adjacent terminals.
In the ""047 patent, since the conductive traces are exposed on the printed circuit board, arranging a ground bus between two printed circuit boards. According to the teaching of the ""047, insulative spacer is arranged to two adjacent printed circuit boards, this will not doubt increase the thickness of the overall dimension of the connector, especially when ground buses are arranged therein.
In addition, when the conductive traces are formed on the printed circuit boards, connecting legs/sockets have to be attached to corresponding conductive trace. This will not doubt complicate the make of the connector.
In the ""047 patent, even the conductive traces formed on both sides of the printed circuited board, since the connecting portion and tail portions are soldered thereto, the it will be unlikely to reach equal impedence between two terminals.
It is desired to provide an electrical connector which provides a smooth surface of the channel being of monolithic construction so as to achieve signal integrity and to minimize the cross-talk and skew in such transmission terminals of the connector.
U.S. Pat Nos. 5,785,534; 5,823,823; 5,893,761; and 6,012,927 issued to Siemens teach another approach of making the high density connector. As typically shown in FIG. 3 of the ""823 patent, the connector generally includes a die-cast housing configured by elements 11a, 12a, and 13a sandwiched between elements 11a and 12a. The element 13a defines a plurality of passageways 14 in which each is assembled with a terminal pair 15 bonded by spacers 16a, 16b. 
One of the problems for the ""823 device is those three-piece terminal block is die-casted which means a fixed dimension has to be determined firstly. If another application is required, another die-cast has to be made to meet the requirement.
The channel of the ""823 device is made by at least two complex shapes, not a smooth surfaces thereby creating several edges-reflection ???, which produce noise.
On the other hand, since the dimension of the elements 11a, 12a and 13a are fixed, it is unlikely that the connector made therefrom can address the Thermal Coefficient of Expansion (TCE) mismatch induced dimensional changes of the PCB.
An object of this invention is to provide an electrical connector configured by a plurality of floated chicklets so as to overcome TCE mismatch induced from changes of printed circuit board.
In order to achieve the object set forth, an electrical connector in accordance with the present invention comprises a plurality of die-cast chicklets defining at least a mounting surface adapted to face a motherboard, and a contacting surface adapted to face a daughterboard. Each chicklet defining at least a waveguide extending between the mounting and contacting surfaces. A plurality of terminals dielectrically supported and received within the waveguides and have contacting ends extending beyond the mounting and contacting surfaces so as to electrically couple the motherboard and the daughterboard.
According to one aspect of the present invention, the terminal is supported by plastic or ceramic beads so as to provide largest air dielectric.
According to another aspect of the present invention, the beads arranged on the terminal according to signal requirements.